93 f53 brake pedal went to floor???

[turretman1st]

driving thru town went to stop at intersection as light turned yellow, brake pedal went all way to floor no brakes pumped and stopped in middle of intersection. pulled over and checked master cylinder resevor full no leakage found under coach. power steering resevor full also found a few drops of powersteering fluid under hydrovac unit. check brake pedal again all working fine. what happened do not ever want it to happen again.
any ideas!!!!!!!!

93 f53 460 28 ft

william

[blackf3504dr]

Quote:

Originally Posted by turretman1st driving thru town went to stop at intersection as light turned yellow, brake pedal went all way to floor no brakes pumped and stopped in middle of intersection. pulled over and checked master cylinder resevor full no leakage found under coach. power steering resevor full also found a few drops of powersteering fluid under hydrovac unit. check brake pedal again all working fine. what happened do not ever want it to happen again. any ideas!!!!!!!! 93 f53 460 28 ft william

Most likely brake fade. When the brakes get hot enough the fluid will boil, it could be you have a caliper hanging up. We had that happen to us while in Ft Wayne IN. while in heavy traffic on US 3.

[Beachcomber]

I tend to agree with Blackf3504dr. Had a similar experience with Workhorse caliper hanging up and boiling fluid. Two caveats though, you should have felt the caliper dragging, and the master cylinder would likely have some brake fluid moisture around the cap if fluid boiled in the lines.er

Beachcomber

[turretman1st]

i hope it was just brake fade, but there was no brakefluid out of the master cylinder. only fliud i found was some drips from hydrovac unit just a little on bottom. been a machinery repairmen my whole life. but this is the only vehicle i have had my hands on with a hydrovac system.
this happening was strange to me.
the hydrovac leak is the first i have found on this unit it has 48000 miles on it

from what i have read thru on this web site there is very good knowledge here. and very helpfull people.

i have another problem i have been trying to get info on i will start a nother thread for.

thankyou
william

[Nick-B]

Hi William and Welcome to the Forum!

I'm going with a bad master cylinder.

If it was brake fade then pumping the pedal would not have stopped him. Notice he said "pumped and stopped".

Replace master cylinder.

[turretman1st]

it worked fine after the episode. if it was the master cylinder it would still be mushy. still im going to change it any way because flooring old master cylinders usually damages the seals due to internal corrosion ( as far as i know this is the factory master cylinder) with the small leak power steering fliud (just a few drops found) should i change the hydrovac unit also

william

[SteveLevin]

I've had (not in a motorhome, but in other vehicles) bad master cylinders that have started off intermittently. One of the ways of typically testing, though, is, at a stop (and in Park!), just hold pressure on the brake pedal for 60 seconds. Typically that shows the fault...in the middle of doing it the pedal will suddenly drop to the floor.

Steve

[53panhead]

I have had the pedal to the floor twice, the first time I was driving in the mountains of NC. I could not pump the pedal to stop, luck on my side when from going down hill to uphill and got stopped. Replaced the master cylinder, no problems for two years, then while traveling to Stone Mountain, GA on a hot day in July 2011 pedal when to floor again. This time still had enough pedal to stop after going half way thru entrance to campground. After getting to camp site and setting up, the pedal after pumping, started to return to normal. Check fluid-no loss. Made return trip home using the brakes as little as possible.
After returning home checked brake lines, replaced brake pads (front and rear), checked calipers and cleaned the pins and recoated with caliper lube. Bleed the brakes untill new brake fluid appeared at all four calipers.
I don't want to have a third time(pedal to the floor) but other than new motorhome don't know what else to do.
1994 Newmar Mountain Aire 37 1/2 ft. with tag axle.
I also checked the braking system for the tag but it is an independent system with its own master cylinder.

[Wanabee FTer]

53panhead,
If the brake pedal went to floor when hot it most likely was caused by a faulty master cylinder unless you found any external leaks in the hydraulic system.
Was the replacement master a new or rebuilt, factory or after market?
Did you bleed all the old fluid from the system when the master was replaced?
I would not trust the master even if it is only 2 years old.

[blackf3504dr]

Quote:

Originally Posted by Wanabee FTer 53panhead, If the brake pedal went to floor when hot it most likely was caused by a faulty master cylinder unless you found any external leaks in the hydraulic system. Was the replacement master a new or rebuilt, factory or after market? Did you bleed all the old fluid from the system when the master was replaced? I would not trust the master even if it is only 2 years old.

I'm betting the problem was over heated brake fluid (brake fade) . When the brake fluid gets hot enough to boil from heavy use it turns to steam which doesn't do much to push the pads towards the rotors.

[Hikerdogs]

Quote:

Originally Posted by blackf3504dr I'm betting the problem was over heated brake fluid (brake fade) . When the brake fluid gets hot enough to boil from heavy use it turns to steam which doesn't do much to push the pads towards the rotors.

I would also suspect the cause to be boiled brake fluid. Have you ever changed the fluid? Ford recommends changing the fluid every 2 years to avoid brake fade problems.

There have been several other posts on this subject over the years. In most cases replacing the brake fluid has eliminated the problem. DOT 3 brake fluid has a dry boiling point of at least 401*, but when it gets "wet" (3% - 4% water saturation) the boiling temperature is lowered to 284*. That's only 72* higher than the temperature water boils at. It doesn't take much braking to raise the fluid temperature high enough for it to boil if it's water saturated.

The dry boiling point of DOT 4 brake fluid is a bit higher at a minimum of 446* and the wet boiling point is also raised to 311* Either will work fine in your motorhome. The boiling temperatures I mentioned are the minimums for voth DOT 3 and DOT 4 fluids. Some of the higher performance versions have higher boiling points.

Just stay away from the DOT5 series fluids. While they do have a higher boiling point than either DOT 3 or 4 fluids they are also silicone based which is not compatible with the rubber seals in your brake system. It is also not hygroscopic meaning if you do get water in the system it will not be absorbed into the fluid. That could cause brake lines to rust out or brakes to fade should the water work itself to the brake cylinders.

It's the least expensive thing to try first and should be done even if you eventually have to replace the master cylinder

[53panhead]

the master cylinder was new aftermarket(advance auto). I don't know if the brakes were bleed enought to remove the old brake fluid from the calipers. when I did the work two week ago I know the brake fluid removed from all calipers.

[53panhead]

the brake fluid I used was Prestone Synthetic Hi Temp Dot 3.
I tend to think the pedal to the floor is heat related. The master cylinder is mounted on frame rail beside and above the exhaust headers(Banks). If that is a problem a lot more people would be having trouble.
If its old brake fluid, again would not more people be reporting trouble.

[Wanabee FTer]

I have heard of heat related master brake cylinder concerns in the automotive world.
I would fabricate a heat shield for the master cylinder, couldn't hurt to add one since the exhaust runs so close to it.